1. Field
The downhole injection system of the present invention is used to inject chemicals such as foaming agents, corrosion inhibitors, and water into wells to treat an observed condition within the well.
2. Background
Wells, particularly those wells which produce hydrocarbons, exhibit various conditions which affect well production or the operability of the equipment inserted into the well. One way of treating such conditions is to inject predetermined amounts of chemical into the well at a downhole location. Such chemical can be pumped from the surface through a capillary tube to a downhole injection valve. Not only is the type of chemical used extremely important, but the injection of a predetermined amount of chemical at a specific rate of application is also critical. If a full column of fluid can be maintained in the capillary tube leading from the chemical pump to the bottom of the well, control of the amount of chemical injected into the well is a relatively simple operation.
However, it has long been recognized by well operators that if the injection pressure or back-pressure exerted on the valve at the bottom of the capillary tubing is not correct, the contents of the capillary tube may actually be siphoned into the well. This siphoning action of the chemical within the capillary tubing is due to the fact that in most systems for injecting chemicals for foaming (for example, in gas wells that are fluid loaded), the hydrostatic pressure at the end of the capillary tubing-is greater than the actual flowing bottom-hole pressure within the well. Therefore, the end of the capillary tubing sees a relative vacuum within the well. This relative, vacuum results in the siphoning of the chemical out of the capillary tube and into the well. This unwanted siphoning of chemical from the capillary tube makes it very difficult to regulate or assure a consistent flow or continuous volume of chemical into the well.
In addition, voids or bubbles in the column of chemical within the capillary tubing will permit well gases and fluids to enter the capillary tubing from the bottom of the well. This movement of gases and fluids into the capillary tubing can result in a plugging of the capillary tubing and/or gas pressure escaping through the capillary tube to the surface. More importantly, the movement of gases and fluids through the capillary tubing caused by voids or bubbles results in an inconsistent application of chemicals such as anti-foaming agents, corrosion inhibitors, etc. The inconsistent application of chemicals adversely affects the application of foamers or corrosion protection of the equipment within the well. In such situations, it has been found that much more chemical must be used than what appears to be actually needed to control a condition within the well. Experience in the chemical treatment of downhole well conditions has shown that a consistent application of chemical provides much greater benefit to the well than an inconsistent or “batch” treatment application of chemical to the bottom of a well.
Prior art valves for the injection of chemicals downhole into a well are described in U.S. Pat. No. 4,441,558 to Welch, et al., U.S. Pat. No. 4,485,876 to Speller; U.S. Pat. No. 4,552,210 to Ross, et al.; U.S. Pat. No. 4,648,457 to Ross, et al.; and U.S. Pat. No. 5,141,056 to Tailby, et al.
Despite the number of chemical injection valves for use downhole within a well which can be found in the prior art, the problem remains to provide a system for inserting a consistent amount of chemical downhole into a well.